Thin films transparent for a light in the visible light region and having electric conductivity are generally used in display systems, e.g., a liquid crystal display and an electroluminescence display, transparent electrodes, e.g., a touch panel, and for the static prevention and cutoff of electromagnetic waves of transparent articles.
As such a transparent conductive thin film, so-called conductive glass comprising a glass plate having formed thereon an indium oxide thin film is conventionally used. However, since glass is used as a base, the conductive glass is inferior in flexibility and processability and cannot be used in some cases according to uses.
Therefore, in recent years, conductive thin films using various kinds of plastic films including polyethylene terephthalate as the base are used for various advantages, e.g., flexibility, processability, impact resistance and light weight. However, since the transparent conductive thin films having plastic films as base layers have a large light reflectivity on thin film surfaces, the transparent conductive think films have a problem of inferior transparency. In addition, there are problems in that the transparent conductive thin films are inferior in durability such as frictioning resistance and flex resistance of the conductive thin films and are damaged during use to cause an increase in electrical resistance or cause disconnection.
In particular, in a touch panel constituted by arranging a pair of upper and lower panel boards, which have conductive thin films, to be opposed to each other via a spacer such that the conductive thin films are opposed to each other, the conductive thin films are brought into contact with each other strongly by pen input from the upper panel board side. Thus, it is desired that the touch panel has satisfactory durability resistible against the contact, that is, durability against pen input.
However, when a panel board having a plastic film as a base layer is used for at least the upper panel board on the pen input side of both the panel boards, there are problems in that, because of insufficient flex resistance or the like of the conductive thin film, the touch panel is inferior in durability against pen input and a durable life as the touch panel is reduced.
To cope with the problems, the applicant has proposed a transparent conductive laminate in which a conductive thin film is formed on one surface of a plastic base layer with thickness of 2 to 120 μm and another plastic base layer is stuck to the other surface via an adhesive layer (see reference 1). This transparent conductive laminate is excellent in durability such as flex resistance. Thus, by using this transparent conductive laminate in at least an upper panel board on a pen input side of a touch panel, it is possible to improve durability against pen input and extend a durable life of the touch panel.
Incidentally, in recent years, since a rim of a touch panel is narrowed in design of the touch panel, there is a strong desire for durability against pen input in the vicinity of electrodes provided at ends of panel boards. In addition, in a touch panel started to be used, as design of a touch panel, not only an upper panel board on a pen input side but also a lower panel board opposed to the upper panel board is made of a plastic base layer and the lower panel board is stuck on a glass board of a display device such as a liquid crystal cell.
Under such circumstances, the proposed transparent conductive laminate cannot sufficiently cope with durability against pen input in the vicinity of the electrodes provided at the ends of the panel boards. The touch panel of the type, in which the lower panel board is also made of the plastic base layer, is particularly inferior in durability against pen input in the vicinity of the electrodes provided at the ends of the panel boards.
[Reference 1] JP 2002-326301 A
In view of such circumstances, the invention relates to a touch panel using a panel board having a base layer comprising a plastic film. It is an object of the invention to improve durability against pen input in the vicinity of electrodes provided at ends of the panel boards (hereinafter referred to as “end push pen input durability”).